More than three million gallons of crude oil may be threatening California's Central Coast. The oil was the cargo of a tanker called the Montebello. Here's the catch: The ship was sunk more than half a century ago by a Japanese submarine, not long after the attack on Pearl Harbor. Now, there's an expedition to determine just how much of a threat the Montebello still poses as she rests about six miles from shore. NPR's Ina Jaffe has our story.

INA JAFFE, BYLINE: It was another stunning day on California's Central Coast. In the water were sea lions, otters, pelicans and more of the varied wildlife this region is known for. On shore, there was a gaggle of folks in uniforms of blue and beige next to the Coast Guard station on Morro Bay. They're members of a combined state and federal task force charged with evaluating the environmental risks posed by the Montebello. The group was put together a couple of years ago at the urging of State Senator Sam Blakeslee.

STATE SENATOR SAM BLAKESLEE: I actually was reading in my local weekly newspaper about this amazing history about a shipwreck that occurred off our coast and that described the fact there still may be three million gallons of oil down at the bottom of the ocean. And no one in all of the 70 years had really stepped up and said it's our responsibility to understand what the threat is to the coast.

JAFFE: In fact, for most of the last 70 years, most people didn't even know the oil tanker was down there.

RICHARD QUINCY: That's why I didn't even talk about it because I was called a liar.

JAFFE: That's Richard Quincy. He's 92 years old and the last surviving member of the crew of the Montebello. They knew the voyage would be dangerous, says Quincy. They even took a vote on whether or not they wanted to go. But with the nation at war...

QUINCY: Everyone had to give something, and that was our decision. Well, this is part of what we do.

JAFFE: On the morning of December 23rd, just before dawn, Quincy was on watch when he saw the outline of a Japanese sub in the water. Then came the torpedo.

QUINCY: It was dark when we got hit.

(SOUNDBITE OF LAUGHTER)

QUINCY: It went so fast. It was hard to keep track of time. We were anxious to get off because we figured it was going to catch fire.

JAFFE: But the ship didn't catch fire because the torpedo struck the Montebello in front of the oil tanks. Everyone on the crew escaped in lifeboats, and the ship went to the bottom nearly intact, says Robert Schwemmer, a marine historian with the National Oceanic and Atmospheric Administration. He's seen the Montebello from a manned submersible twice, once in 1996, again in 2003.

ROBERT SCHWEMMER: The ship looked like it just left the dock, except the fact that the upper wheelhouse is missing. So we have 90 percent of the Montebello sitting there squarely on its keel. The question is, is the oil on board?

JAFFE: Schwemmer called on his cell phone from the Nanuq, which is the mother ship, so to speak, for the investigation that's supposed to answer that question. It's owned by Global Diving & Salvage, and it sailed down from Seattle and then basically parked above the Montebello. On board are unmanned remote-operated vehicles or ROVs that are being sent below to study the wreck. Schwemmer said they can do a better job than the manned submersibles. [POST-BROADCAST CORRECTION: The Nanuq is owned by Edison Chouest Offshore, not Global Diving & Salvage.]

SCHWEMMER: When you do a submersible survey, you're always moving. The ROV allows us to actually come up to different locations and stay on station and study them in more detail.

JAFFE: And a detailed assessment of the threat posed by the Montebello is important to more than just California's coast. Kerry Walsh, project manager with Global Diving & Salvage, says that's because the Montebello is not the only potentially polluting wreck that's been identified by the National Oceanic and Atmospheric Administration.

KERRY WALSH: This wreck represents the first one in many hundreds of wrecks that NOAA is looking at that are around the United States that have oil in them.

JAFFE: Those wrecks are strewn along both the East and West Coasts, and the detailed examination of the Montebello could be a blueprint for evaluating them, says Walsh. There are a lot of steps in that evaluation. First, the ROV cleans portions of the Montebello's hull, then uses ultrasound to measure the thickness of the metal.

WALSH: Once that's done, then we bring in the nuclear tool, which is a diagnostic scan device, and we press that up against the hull. And we measure through the steel, and we can detect by the return signal from the neutron backscatter what's behind it.

JAFFE: So you would get one kind of signal if it was seawater and another kind of signal if it was oil?

WALSH: Correct.

JAFFE: But they'll want to confirm those results, so Walsh says Global Diving & Salvage is also taking samples from the cargo tanks with a tool they've invented that both drills into the tank and plugs the hole.

WALSH: And if that doesn't work, we have another device that's a magnetic patch that will seal it up forever.

JAFFE: And if it turns out that the Montebello is still carrying her cargo of crude, the biggest challenge of all may be figuring out how to protect the sensitive central coast from the threat lying 900 feet below the waves. Ina Jaffe, NPR News.

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